I believe the answer you're looking for extends beyond just jQuery. While JavaScript/jQuery will certainly be involved for interacting with the Google map object, the client-side languages may not be powerful enough to complete this task.
The most complete solution I've found to this question is actually provided by Google:
That page provides detailed instructions on how to create a "Store locator" (or whatever you're locating) using PHP, MySQL, and Google Maps.
That page also links to a good article detailing the algorithms involved:
The calculations are fairly in-depth, but the page does a great job of explaining the logic and even provides JavaScript in case you'd like to create your own solution.
Good luck!